1. Field of the Invention
The present invention relates to a process for manufacturing elastomeric components of a tyre for vehicle wheels.
2. Description of the Related Art
Manufacturing of tyres for vehicle wheels involves formation of a carcass structure essentially made up of one or more carcass plies of a substantially toroidal shape and having their axially opposite side edges in engagement with respective annular reinforcing elements usually referred to as “bead cores”.
Provided on the carcass structure at a radially external position, is a belt structure comprising one or more belt strips in the form of a closed ring and essentially made up of textile or metallic cords suitably oriented with respect to each other and the cords belonging to adjacent carcass plies.
At a radially external position of the belt structure, a tread band is provided which usually consists of a band of elastomeric material of suitable thickness.
Finally, on the opposite sides of the tyre there is a pair of sidewalls, each of them covering a side portion of the tyre included between a so-called shoulder region disposed close to the corresponding side edge of the tread band, and a so-called bead located at the respective bead core.
To the aims of the present invention it should be pointed out that by the term “elastomeric material” it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably this composition further comprises additives such as a cross-linking and/or plasticizing agent, for example. Due to the presence of the cross-linking agent, this material can be cross-linked through heating so as to form the final article of manufacture.
Traditional production methods essentially provide for the above listed tyre components to be first made separated from each other, to be then assembled during a tyre building step.
However, there is a general tendency in the present technologies to resort to production methodologies enabling production and storage of semi-finished products to be minimised or possibly eliminated.
For the purpose, manufacturing processes have been proposed that aim at obtaining given tyre components such as tread band, sidewalls or others, by laying onto a toroidal support carrying the tyre being worked, a continuous elongated element of elastomeric material of a reduced section as compared with that of the component to be obtained, which elongated element is such arranged as to form, around the rotation axis of the tyre, a plurality of consecutive coils disposed in side by side and/or overlapped relationship so as to define the component itself in its final configuration.
WO 01/36185 A1 in the name of the same Applicant, discloses a method of manufacturing components of elastomeric material in a tyre for vehicle wheels comprising the steps of: feeding a continuous elongated element from a delivery member disposed close to a toroidal support for application of said elongated element onto the toroidal support itself; giving the toroidal support a rotatory motion around its geometrical rotation axis, so that the elongated element is circumferentially distributed on the toroidal support; carrying out controlled relative displacements for transverse distribution between the toroidal support and the delivery member to form a tyre component with said elongated element which is defined by a plurality of coils laid down in side by side or mutual overlapped relationship according to a preestablished deposition pattern depending on a predetermined cross-section outline to be given to said component. In particular said document teaches that if the peripheral speed of the toroidal support at the point of application of an elongated element is such controlled that a conveniently higher value than the feeding speed of the elongated element itself by the delivery member is maintained, adhesion of the applied elongated element is greatly improved and important advantages in terms of operating flexibility are achieved. In particular, the possibility of conveniently modifying the cross-section sizes of the elongated element is obtained so as to adapt the latter to the thickness of the component to be made, at the different points of the cross-section outline of the component itself.
Document EP 1 279 486 A2 discloses a method of manufacturing a shaped rubber element through extrusion of a strip by an extrusion process comprising a screw extruder, a gear pump and an extruder head having an extrusion nozzle, said units being connected in series with each other. Said method comprises the steps of: feeding a rubber strip onto a rotating support, along a passage extending from said screw extruder to said extrusion nozzle of the extruder head, wherein said passage is substantially a straight passage; and directly or indirectly applying the rubber strip to an outer peripheral surface of the support.
Document EP 1 201 414 A2 discloses a method of manufacturing a tyre comprising: assembling the non-vulcanized rubber components to form a green tyre, vulcanizing the green tyre and wrapping a non-vulcanized rubber strip in such a manner that windings on the whole have a shape of a predetermined cross-section for at least one non-vulcanized rubber component so as to form at least one of the non-vulcanized rubber components.
Document EP 1 211 057 A2 discloses a method of manufacturing a tyre in which, during formation of a green tyre, at least one constituent element, the sidewalls for example, is formed through expansion in a radially external direction of a central portion of a substantially cylindrical carcass band, a non-vulcanized rubber strip being then wound up, junction of the rubber strip taking place on an outer peripheral surface of the expanded carcass band.